InGaP heterojunction barrier solar cells

Abstract

A new solar cell structure called a heterojunction barrier solar cell is described. As with previously reported quantum-well and quantum-dot solar cell structures, a layer of narrow band-gap material, such as GaAs or indium-rich InGaP, is inserted into the depletion region of a wide band-gap PN junction. Rather than being thin, however, the layer of narrow band-gap material is about 400-430 nm wide and forms a single, ultrawide well in the depletion region. Thin (e.g., 20-50 nm), wide band-gap InGaP barrier layers in the depletion region reduce the diode dark current. Engineering the electric field and barrier profile of the absorber layer, barrier layer, and p-type layer of the PN junction maximizes photogenerated carrier escape. This new twist on nanostructured solar cell design allows the separate optimization of current and voltage to maximize conversion efficiency.

What is claimed is: 
     
       1. A solar cell device structure, comprising:
 a) a single, wide band-gap PN junction including a p-type emitter layer, an n-type back surface field layer, and a depletion region between the p-type emitter layer and the n-type layer; 
 b) a narrow band gap absorber layer within the depletion region, the narrow band gap absorber layer having a thickness between about 100 nm and 1 micron; 
 c) an InGaP barrier layer within the depletion region that directly adjoins the emitter layer and has a thickness between about 20 nm and about 50 nm; 
 wherein the narrow band gap absorber layer forms a single, ultrawide well in the depletion region. 
 
     
     
       2. The solar cell of  claim 1 , wherein the PN junction has a band-gap of about 1.9 eV. 
     
     
       3. The solar cell of  claim 1 , wherein the PN junction includes at least one of an AlGaAs alloy and an InGaP alloy. 
     
     
       4. The solar cell of  claim 1 , wherein the p-type layer is a graded AlGaAs layer. 
     
     
       5. The solar cell of  claim 1 , wherein the PN junction is nearly lattice-matched, indium-rich InGaP. 
     
     
       6. The solar cell of  claim 1 , wherein the absorber layer has a band-gap of about 1.42 eV. 
     
     
       7. The solar cell of  claim 1 , wherein the absorber layer includes at least one of an InGaP alloy, a GaAs alloy, and an InGaAs alloy. 
     
     
       8. The solar cell of  claim 1 , wherein the InGaP barrier layer has a band-gap of equal to or greater than about 1.93 eV. 
     
     
       9. The solar cell of  claim 1 , wherein the InGaP barrier layer is lattice-mismatched and gallium rich. 
     
     
       10. The solar cell of  claim 1 , wherein the total thickness of the InGaP barrier layer and the absorber layer is approximately 500 nm. 
     
     
       11. The solar cell of  claim 1 , further including InGaAs wells in the absorber layer. 
     
     
       12. The solar cell of  claim 11 , further including an AlGaAs window disposed over the p-type layer. 
     
     
       13. A method of making a solar cell device structure, comprising the steps of:
 a) providing a single junction wide band-gap PIN diode that includes a p-type emitter layer, an n-type back surface field layer, and a depletion region containing an absorber layer of narrow band-gap material between the p-type and the n-type layers; 
 b) inserting an InGaP barrier layer between the p-type and n-type layers directly adjoining the p-type emitter layer; 
 wherein the narrow band gap absorber layer is between about 100 nm and 1 micron thick; 
 wherein the InGaP barrier layer is between about 20 nm thick and about 50 nm thick: 
 wherein the narrow band gap absorber layer forms a single, ultrawide well in the depletion region. 
 
     
     
       14. The method of  claim 13 , wherein the band-gap of the PIN diode is about 1.9 eV. 
     
     
       15. The method of  claim 13 , wherein the PIN diode is an InGaP PIN diode or an AlGaAs PIN diode. 
     
     
       16. The method of  claim 15 , further including replacing the absorber layer with a GaAs absorber layer or an InGaAs absorber layer. 
     
     
       17. The method of  claim 13 , wherein the p-type layer is a graded AlGaAs layer. 
     
     
       18. The method of  claim 13 , wherein the absorber layer has a band-gap energy of about 1.42 eV. 
     
     
       19. The method of  claim 13 , wherein the PIN diode is includes nearly lattice-matched, slightly indium-rich InGaP. 
     
     
       20. The method of  claim 13 , wherein the InGaP barrier layer has a band-gap of equal to or greater than about 1.93 eV. 
     
     
       21. The method of  claim 13 , wherein the InGaP barrier layer is lattice-mismatched and slightly gallium rich. 
     
     
       22. The method of  claim 13 , wherein the total thickness of the InGaP barrier layer and the absorber layer is approximately 500 nm. 
     
     
       23. The method of  claim 13 , further including tailoring characteristics of the barrier layer and the absorber layer to maximize a photocurrent at forward bias. 
     
     
       24. The method of  claim 13 , further including inserting InGaAs wells into the absorber layer. 
     
     
       25. The method of  claim 13 , further including disposing an AlGaAs window over the p-type layer.